Communication System with Remote Activation

ABSTRACT

The system of the present invention includes a conductive element, an electronic component, and a partial power source in the form of dissimilar materials. Upon contact with a conducting fluid, a voltage potential is created and the power source is completed, which activates the system. The electronic component controls the conductance between the dissimilar materials to produce a unique current signature. The system can also measure the conditions of the environment surrounding the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 12/564,017, filed on Sep. 21, 2009 and entitled “Communication System with Partial Power Source”, published on Apr. 1, 2010 as U.S. Publication No. US2010-0081894A1, which is a continuation-in-part application of U.S. patent application Ser. No. 11/912,475 filed Jun. 23, 2008 and entitled “Pharma-Informatics System”, published on Nov. 20, 2008 as U.S. Publication No. 2008-0284599A1 which application is a 371 application of PCT Application No. PCT/US06/16370 filed Apr. 28, 2006 and entitled “Pharma-Informatics System”; which application pursuant to 35 U.S.C. §119 (e), claims priority to the filing dates of: U.S. Provisional Patent Application Ser. No. 60/676,145 filed Apr. 28, 2005 and entitled “Pharma-Informatics System”; U.S. Provisional Patent Application Ser. No. 60/694,078, filed Jun. 24, 2005, and entitled “Pharma-Informatics System”; U.S. Provisional Patent Application Ser. No. 60/713,680 filed Sep. 1, 2005 and entitled “Medical Diagnostic And Treatment Platform Using Near-Field Wireless Communication Of Information Within A Patient's Body”; and U.S. Provisional Patent Application Ser. No. 60/790,335 filed Apr. 7, 2006 and entitled “Pharma-Informatics System”; the disclosures of which are herein incorporated by reference.

This application is related to the following US Applications filed concurrently herewith, the disclosures of which are incorporated herein by reference: U.S. application Ser. No. ______ COMMUNICATION SYSTEM WITH MULTIPLE TYPES OF POWER (Attorney Docket No. PRTS-01000N2CIP2 (PRO-148)); U.S. application Ser. No. ______ COMMUNICATION SYSTEM USING AN IMPLANTABLE DEVICE (Attorney Docket No. PRTS-01000N2CIP3 (PRO-149)); U.S. application Ser. No. ______ COMMUNICATION SYSTEM WITH ENHANCED PARTIAL POWER AND METHOD OF MANUFACTURING SAME (Attorney Docket No. PRTS-01000N2CIP4 (PRO-150)); U.S. application Ser. No. ______ COMMUNICATION SYSTEM USING POLYPHARMACY CO-PACKAGED MEDICATION DOSING UNIT (Attorney Docket No. PRTS-01000N2CIP5 (PRO-151)); and U.S. application Ser. No. ______ Communication System Incorporated in an INGESTIBLE PRODUCT (Attorney Docket No. PRTS-01000N2CIP6 (PRO-152)).

FIELD

The present invention is related to communication systems for detection of an event. More specifically, the present disclosure includes a system that includes a device with various power sources and communication schemes.

INTRODUCTION

Ingestible devices that include electronic circuitry have been proposed for use in a variety of different medical applications, including both diagnostic and therapeutic applications. These devices typically require an internal power supply for operation. Examples of such ingestible devices are ingestible electronic capsules which collect data as they pass through the body, and transmit the data to an external receiver system. An example of this type of electronic capsule is an in-vivo video camera. The swallowable capsule includes a camera system and an optical system for imaging an area of interest onto the camera system. The transmitter transmits the video output of the camera system and the reception system receives the transmitted video output. Other examples include an ingestible imaging device, which has an internal and self-contained power source, which obtains images from within body lumens or cavities. The electronic circuit components of the device are enclosed by an inert indigestible housing (e.g. glass housing) that passes through the body internally. Other examples include an ingestible data recorder capsule medical device. The electronic circuits of the disclosed device (e.g. sensor, recorder, battery etc.) are housed in a capsule made of inert materials.

In other examples, fragile radio frequency identification (RFID) tags are used in drug ingestion monitoring applications. In order for the RFID tags to be operational, each application/tag requires an internal power supply. The RFID tags are antenna structures that are configured to transmit a radio-frequency signal through the body.

The problem these existing devices pose is that the power source is internal to device and such power sources are bulky, costly to produce and potentially harmful to the surrounding environment if the power source leaks or is damaged. Additionally, having antennas extending from the device is a concern as related to the antennas getting damaged or causing a problem when the device is used in-vivo. Therefore, what is needed is suitable system with circuitry that eliminates the need for an internal power source and antennas.

SUMMARY

The present disclosure includes a system for producing a unique signature that indicates the occurrence of an event. The system includes circuitry and components that can be placed within certain environments that include a conducting fluid. One example of such an environment is inside a container that houses the conducting fluid, such as a sealed bag with a solution, which includes an IV bag. Another example is within the body of a living organism, such as an animal or a human. The systems are ingestible and/or digestible or partially digestible. The system includes dissimilar materials positioned on the framework such that when a conducting fluid comes into contact with the dissimilar materials, a voltage potential difference is created. The voltage potential difference, and hence the voltage, is used to power up control logic that is positioned within the framework. Ions or current flows from the first dissimilar material to the second dissimilar material via the control logic and then through the conducting fluid to complete a circuit. The control logic controls the conductance between the two dissimilar materials and, hence, controls or modulates the conductance of the system.

As the ingestible circuitry is made up of ingestible, and even digestible, components, the ingestible circuitry results in little, if any, unwanted side effects, even when employed in chronic situations. Examples of the range of components that may be included are: logic and/or memory elements; effectors; a signal transmission element; and a passive element, such as a resistor or inductor. The one or more components on the surface of the support may be laid out in any convenient configuration. Where two or more components are present on the surface of the solid support, interconnects may be provided. All of the components and the support of the ingestible circuitry are ingestible, and in certain instances digestible or partially digestible.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a pharmaceutical product with an event indicator system according to the teaching of the present invention, wherein the product and the event indicator system combination are within the body.

FIG. 2A shows the pharmaceutical product of FIG. 1 with the event indicator system on the exterior of the pharmaceutical product.

FIG. 2B shows the pharmaceutical product of FIG. 1 with the event indicator system positioned inside the pharmaceutical product.

FIG. 2C shows a capsule with the event indicator system positioned inside in accordance with one aspect of the present invention.

FIG. 2D shows a capsule with the event indicator system positioned inside in accordance with one aspect of the present invention.

FIG. 2E shows a capsule with the event indicator system positioned inside in accordance with one aspect of the present invention.

FIG. 2F is an exploded view of the event indicator system.

FIG. 3 is a block diagram representation of one aspect of the event indicator system with dissimilar metals positioned on opposite ends.

FIG. 4 is a block diagram representation of another aspect of the event indicator system with dissimilar metals positioned on the same end and separated by a non-conducting material.

FIG. 5 shows ionic transfer or the current path through a conducting fluid when the event indicator system of FIG. 3 is in contact with conducting liquid and in an active state.

FIG. 5A shows an exploded view of the surface of dissimilar materials of FIG. 5.

FIG. 5B shows the event indicator system of FIG. 5 with a pH sensor unit.

FIG. 6 is a block diagram illustration of one aspect of the control device used in the system of FIGS. 3 and 4.

DETAILED DESCRIPTION

The present disclosure includes multiple aspects for indicating the occurrence of an event. As described in more detail below, a system of the present invention is used with a conducting fluid to indicate the event marked by contact between the conducting fluid and the system. For example, the system of the present disclosure may be used with pharmaceutical product and the event that is indicated is when the product is taken or ingested. The term “ingested” or “ingest” or “ingesting” is understood to mean any introduction of the system internal to the body. For example, ingesting includes simply placing the system in the mouth all the way to the descending colon. Thus, the term ingesting refers to any instant in time when the system is introduced to an environment that contains a conducting fluid. Another example would be a situation when a non-conducting fluid is mixed with a conducting fluid. In such a situation the system would be present in the non-conduction fluid and when the two fluids are mixed, the system comes into contact with the conducting fluid and the system is activated. Yet another example would be the situation when the presence of certain conducting fluids needed to be detected. In such instances, the presence of the system, which would be activated, within the conducting fluid could be detected and, hence, the presence of the respective fluid would be detected.

Referring again to the instance where the system is used with the product that is ingested into the living organism, when the product that includes the system is taken or ingested, the device comes into contact with the conducting liquid of the body. When the system of the present invention comes into contact with the body fluid, a voltage potential is created and the system is activated. A portion of the power source is provided by the device, while another portion of the power source is provided by the conducting fluid, which is discussed in detail below.

Referring now to FIG. 1, an ingestible product 14 that includes a system of the present invention is shown inside the body. The product 14 is configured as an orally ingestible pharmaceutical formulation in the form of a pill or capsule. Upon ingestion, the pill moves to the stomach. Upon reaching the stomach, the product 14 is in contact with stomach fluid 18 and undergoes a chemical or electrochemical reaction with the various materials in the stomach fluid 18, such as hydrochloric acid and other digestive agents. The system of the present invention is discussed in reference to a pharmaceutical environment. However, the scope of the present invention is not limited thereby. The present invention can be used in any environment e.g., outside a body, where a conducting fluid is present or becomes present through mixing of two or more components that result in a conducting liquid.

Referring now to FIG. 2A, a pharmaceutical product 10, similar to the product 14 of FIG. 1, is shown with a system 12, such as an ingestible event marker or an ionic emission module (IEM). The scope of the present invention is not limited by the shape or type of the product 10. For example, it will be clear to one skilled in the art that the product 10 can be a capsule, a time-release oral dosage, a tablet, a gel cap, a sub-lingual tablet, or any oral dosage product that can be combined with the system 12. In the referenced aspect, the product 10 has the system 12 secured to the exterior using known methods of securing micro-devices to the exterior of pharmaceutical products. Example of methods for securing the micro-device to the product is disclosed in U.S. Provisional application Ser. No. 12/741,583 filed on Jan. 5, 2010 and entitled “HIGH-THROUGHPUT PRODUCTION OF INGESTIBLE EVENT MARKERS” also filed as PCT Application No. PCT/US10/20142 dated Jan. 5, 2010 and published as WO 2010/080765 dated Jul. 15, 2010 as well as U.S. Provisional Application No. 61/177,611 filed on May 12, 2009 and entitled “INGESTIBLE EVENT MARKERS COMPRISING AN IDENTIFIER AND AN INGESTIBLE COMPONENT”, also filed as PCT Application No. PCT/US10/34186 dated May 10, 2010 and published as WO 2010/132331 dated Nov. 18, 2010 the entire disclosure of each is incorporated herein by reference. Once ingested, the system 12 comes into contact with body liquids and the system 12 is activated. The system 12 uses the voltage potential difference to power up and thereafter modulates conductance to create a unique and identifiable current signature. Upon activation, the system 12 controls the conductance and, hence, current flow to produce the current signature.

There are various reasons for delaying the activation of the system 12. In order to delay the activation of the system 12, the system 12 may be coated with a shielding material or protective layer. The layer is dissolved over a period of time, thereby allowing the system 12 to be activated when the product 10 has reached a target location.

Referring now to FIG. 2B, a pharmaceutical product 20, similar to the product 14 of FIG. 1, is shown with a system 22, such as an ingestible event marker or an identifiable emission module. The scope of the present invention is not limited by the environment to which the system 22 is introduced. For example, the system 22 can be enclosed in a capsule that is taken in addition to/independently from the pharmaceutical product. The capsule may be simply a carrier for the system 22 and may not contain any product. Furthermore, the scope of the present invention is not limited by the shape or type of product 20. For example, it will be clear to one skilled in the art that the product 20 can be a capsule, a time-release oral dosage, a tablet, a gel capsule, a sub-lingual tablet, or any oral dosage product. In the referenced aspect, the product 20 has the system 22 positioned inside or secured to the interior of the product 20. In one aspect, the system 22 is secured to the interior wall of the product 20. When the system 22 is positioned inside a gel capsule, then the content of the gel capsule is a non-conducting gel-liquid. On the other hand, if the content of the gel capsule is a conducting gel-liquid, then in an alternative aspect, the system 22 is coated with a protective cover to prevent unwanted activation by the gel capsule content. If the content of the capsule is a dry powder or microspheres, then the system 22 is positioned or placed within the capsule. If the product 20 is a tablet or hard pill, then the system 22 is held in place inside the tablet. Once ingested, the product 20 containing the system 22 is disintegrated and/or dissolved. The system 22 comes into contact with body liquids and the system 22 is activated. Depending on the product 20, the system 22 may be positioned in either a near-central or near-perimeter position depending on the desired activation delay between the time of initial ingestion and activation of the system 22. For example, a central position for the system 22 means that it will take longer for the system 22 to be in contact with the conducting liquid and, hence, it will take longer for the system 22 to be activated. Therefore, it will take longer for the occurrence of the event to be detected.

Referring now to FIG. 2C, in accordance with one aspect of the present invention, a capsule 11 is shown with a cavity 11 a therein. The capsule 11 is shown as an empty capsule in accordance with one aspect of the present invention. Inside the cavity is a system 12 a, which is similar to the systems 12 and 22 of FIGS. 2A and 2B, respectively. As the capsule 11 is introduced to or comes into contact with a conducting fluid, the capsule 11 breaks apart or disintegrates or dissolves to allow the system to be released from the environment.

Referring now to FIG. 2D, the capsule 11 is shown with the system 12 a along with a material 13 inserted into the cavity 11 a. The material 13 can be activated to expand and cause the capsule 11 to break apart. In accordance with one aspect of the present invention, the activation of the material 13 is controlled by the system 12 a. The system 12 a, as shown in FIG. 2E below, receives a signal from an external source which may be inside the body, on the body or outside the body and in response to the signal, is able to activate the material 13 to cause the material 12 to expand. For example, in accordance with one aspect of the present invention, the material 13 is an electroactive material that is selected to be reactive to an electrical signal such that the properties change when exposed to a voltage potential or current. An electroactive material or matrix includes a material whose properties, such as physical dimensions or solubility, change in response to an applied voltage or current. Examples of electroactive materials include: polyvinylidene fluoride (PVDF), perfluorinated sulfouic acid (Nafion™), perfluorinated carboxylic acid (Flemion™), cellulose, a polymer matrix (for example polyethylene oxide or cellulose) containing a salt (eg a salt containing a multivalent ion such as Fe³⁺) or a protein. In accordance with another aspect of the present invention, the system 12 a includes a plunger that releases a chemical or compound into the material 11 a to cause a chemical reaction that causes the material 11 a to expand.

Referring now to FIG. 2E, the capsule 11 is shown with the system 12 a in greater detail. The system 12 a includes a unit 12 b secured to the system 12 a. In accordance with one aspect of the present invention, the unit 12 b includes a housing that defines a cavity 12 c. In one example, the cavity 12 c can be filled with a chemical or a compound that is released into the cavity 11 a when the cavity 11 a is filled with the material 13 to initiate a reaction that causes the material 13 to expand. Referring now also to FIG. 2F, in another example, the cavity 12 c includes a solid object that acts like a needle or a rod. The object is mechanically pushed out of the cavity 12 c in the direction AA as shown. The object is then able to push through the wall of the capsule 11 and cause the wall to tear or break apart. This facilitates separation of the system 12 a from the capsule 11 and allows the system 12 a to come into contact with the surrounding environment and become activated. Thus, the unit 12 b is able to control activation of the system 12 a.

In accordance with one aspect of the present invention, the unit 12 b includes a communication module that can either receive, transmit, or receive and transmit. Thus, the unit 12 b can act as a secondary communication module, as discussed in detail below with respect to FIG. 5 and element 75. The unit 12 b can receive control signals from and external source, in accordance with one aspect of the present invention. In accordance with another aspect, the unit 12 b can send signals to an external source. In accordance with yet another aspect of the present invention, the unit 12 b acts as a transceiver and is able to receive and send signals to external devices. The unit 12 b is also in communication with the other components of the system 12 a as discussed in detail below.

Referring now to FIG. 3, in one aspect, the systems 12 and 22 of FIGS. 2A and 2B, respectively, are shown in more detail as system 30. The system 30 can be used in association with any pharmaceutical product, as mentioned above, to determine when a patient ingests the pharmaceutical product. As indicated above, the scope of the present invention is not limited by the environment and the product that is used with the system 30. For example, the system 30 may be placed within a capsule and the capsule is placed within the conducting liquid. The capsule would then dissolve over a period of time and release the system 30 into the conducting liquid. Thus, in one aspect, the capsule would contain the system 30 and no product. Such a capsule may then be used in any environment where a conducting liquid is present and with any product. For example, the capsule may be dropped into a container filled with jet fuel, salt water, tomato sauce, motor oil, or any similar product. Additionally, the capsule containing the system 30 may be ingested at the same time that any pharmaceutical product is ingested in order to record the occurrence of the event, such as when the product was taken.

In the specific example of the system 30 combined with the pharmaceutical product, as the product or pill is ingested, the system 30 is activated. The system 30 controls conductance to produce a unique current signature that is detected, thereby signifying that the pharmaceutical product has been taken. The system 30 includes a resistance 31 between the V^(high) and ground 52. The resistive element includes a known quantity and represents a voltage drop between V_(high) and ground. This known quantity is used to determine the impedance of the surrounding environment as noted with respect to FIG. 5 below and unit 75 a.

The system 30 includes a framework 32. The framework 32 is a chassis for the system 30 and multiple components are attached to, deposited upon, or secured to the framework 32. In this aspect of the system 30, an ingestible or digestible material 34 is physically associated with the framework 32. The material 34 may be chemically deposited on, evaporated onto, secured to, or built-up on the framework all of which may be referred to herein as “deposit” with respect to the framework 32. The material 34 is deposited on one side of the framework 32. The materials of interest that can be used as material 34 include, but are not limited to: Cu or Cul. The material 34 is deposited by physical vapor deposition, electrodeposition, or plasma deposition, among other protocols. The material 34 may be from about 0.05 to about 500 μm thick, such as from about 5 to about 100 μm thick. The shape is controlled by shadow mask deposition, or photolithography and etching. Additionally, even though only one region is shown for depositing the material, each system 30 may contain two or more electrically unique regions where the material 34 may be deposited, as desired.

At a different side, which is the opposite side as shown in FIG. 3, another digestible material 36 is deposited, such that materials 34 and 36 are dissimilar and are insulated from each other. Although not shown, the different side selected may be the side next to the side selected for the material 34. The scope of the present invention is not limited by the side selected and the term “different side” can mean any of the multiple sides that are different from the first selected side. Furthermore, even though the shape of the system is shown as a square, the shape maybe any geometrically suitable shape. Material 34 and 36 are selected such that they produce a voltage potential difference when the system 30 is in contact with conducting liquid, such as body fluids. The materials of interest for material 36 include, but are not limited to: Mg, Zn, or other electronegative metals. As indicated above with respect to the material 34, the material 36 may be chemically deposited on, evaporated onto, secured to, or built-up on the framework. Also, an adhesion layer may be necessary to help the material 36 (as well as material 34 when needed) to adhere to the framework 32. Typical adhesion layers for the material 36 are Ti, TiW, Cr or similar material. Anode material and the adhesion layer may be deposited by physical vapor deposition, electrodeposition or plasma deposition. The material 36 may be from about 0.05 to about 500 μm thick, such as from about 5 to about 100 μm thick. However, the scope of the present invention is not limited by the thickness of any of the materials nor by the type of process used to deposit or secure the materials to the framework 32.

According to the disclosure set forth, the materials 34 and 36 can be any pair of materials with different electrochemical potentials. Additionally, in the aspects wherein the system 30 is used in-vivo, the materials 34 and 36 may be vitamins that can be absorbed. More specifically, the materials 34 and 36 can be made of any two materials appropriate for the environment in which the system 30 will be operating. For example, when used with an ingestible product, the materials 34 and 36 are any pair of materials with different electrochemical potentials that are ingestible. An illustrative example includes the instance when the system 30 is in contact with an ionic solution, such as stomach acids. Suitable materials are not restricted to metals, and in certain aspects the paired materials are chosen from metals and non-metals, e.g., a pair made up of a metal (such as Mg) and a salt (such as CuCl or Cul). With respect to the active electrode materials, any pairing of substances—metals, salts, or intercalation compounds—with suitably different electrochemical potentials (voltage) and low interfacial resistance are suitable.

Materials and pairings of interest include, but are not limited to, those reported in Table 1 below. In one aspect, one or both of the metals may be doped with a non-metal, e.g., to enhance the voltage potential created between the materials as they come into contact with a conducting liquid. Non-metals that may be used as doping agents in certain aspects include, but are not limited to: sulfur, iodine and the like. In another aspect, the materials are copper iodine (Cul) as the anode and magnesium (Mg) as the cathode. Aspects of the present invention use electrode materials that are not harmful to the human body.

TABLE 1 Anode Cathode Metals Magnesium, Zinc Sodium, Lithium Iron Salts Copper salts: iodide, chloride, bromide, sulfate, formate, (other anions possible) Fe³⁺ salts: e.g. orthophosphate, pyrophosphate, (other anions possible) Oxygen or Hydrogen ion (H+) on platinum, gold or other catalytic surfaces Intercalation Graphite with Li, Vanadium oxide compounds K, Ca, Na, Mg Manganese oxide

Thus, when the system 30 is in contact with the conducting liquid, a current path, an example is shown in FIG. 5, is formed through the conducting liquid between material 34 and 36. A control device 38 is secured to the framework 32 and electrically coupled to the materials 34 and 36. The control device 38 includes electronic circuitry, for example control logic that is capable of controlling and altering the conductance between the materials 34 and 36.

The voltage potential created between the materials 34 and 36 provides the power for operating the system as well as produces the current flow through the conducting fluid and the system. In one aspect, the system operates in direct current mode. In an alternative aspect, the system controls the direction of the current so that the direction of current is reversed in a cyclic manner, similar to alternating current. As the system reaches the conducting fluid or the electrolyte, where the fluid or electrolyte component is provided by a physiological fluid, e.g., stomach acid, the path for current flow between the materials 34 and 36 is completed external to the system 30; the current path through the system 30 is controlled by the control device 38. Completion of the current path allows for the current to flow and in turn a receiver, not shown, can detect the presence of the current and recognize that the system 30 has been activate and the desired event is occurring or has occurred.

In one aspect, the two materials 34 and 36 are similar in function to the two electrodes needed for a direct current power source, such as a battery. The conducting liquid acts as the electrolyte needed to complete the power source. The completed power source described is defined by the electrochemical reaction between the materials 34 and 36 of the system 30 and enabled by the fluids of the body. The completed power source may be viewed as a power source that exploits electrochemical conduction in an ionic or a conducting solution such as gastric fluid, blood, or other bodily fluids and some tissues. Additionally, the environment may be something other than a body and the liquid may be any conducting liquid. For example, the conducting fluid may be salt water or a metallic based paint.

In certain aspects, these two materials are shielded from the surrounding environment by an additional layer of material. Accordingly, when the shield is dissolved and the two dissimilar materials are exposed to the target site, a voltage potential is generated.

In certain aspects, the complete power source or supply is one that is made up of active electrode materials, electrolytes, and inactive materials, such as current collectors, packaging, etc. The active materials are any pair of materials with different electrochemical potentials. Suitable materials are not restricted to metals, and in certain aspects the paired materials are chosen from metals and non-metals, e.g., a pair made up of a metal (such as Mg) and a salt (such as Cul). With respect to the active electrode materials, any pairing of substances—metals, salts, or intercalation compounds—with suitably different electrochemical potentials (voltage) and low interfacial resistance are suitable.

A variety of different materials may be employed as the materials that form the electrodes. In certain aspects, electrode materials are chosen to provide for a voltage upon contact with the target physiological site, e.g., the stomach, sufficient to drive the system of the identifier. In certain aspects, the voltage provided by the electrode materials upon contact of the metals of the power source with the target physiological site is 0.001 V or higher, including 0.01 V or higher, such as 0.1 V or higher, e.g., 0.3 V or higher, including 0.5 volts or higher, and including 1.0 volts or higher, where in certain aspects, the voltage ranges from about 0.001 to about 10 volts, such as from about 0.01 to about 10 V.

Referring again to FIG. 3, the materials 34 and 36 provide the voltage potential to activate the control device 38. Once the control device 38 is activated or powered up, the control device 38 can alter conductance between the materials 34 and 36 in a unique manner. By altering the conductance between materials 34 and 36, the control device 38 is capable of controlling the magnitude of the current through the conducting liquid that surrounds the system 30. This produces a unique current signature that can be detected and measured by a receiver (not shown), which can be positioned internal or external to the body. In addition to controlling the magnitude of the current path between the materials, non-conducting materials, membrane, or “skirt” are used to increase the “length” of the current path and, hence, act to boost the conductance path, as disclosed in the U.S. patent application Ser. No. 12/238,345 entitled, “In-Body Device with Virtual Dipole Signal Amplification” filed Sep. 25, 2008, and published as 2009-0082645 A1 dated Mar. 26, 2009 the entire content of which is incorporated herein by reference. Alternatively, throughout the disclosure herein, the terms “non-conducting material”, “membrane”, and “skirt” are used interchangeably with the term “current path extender” without impacting the scope or the present aspects and the claims herein. The skirt, shown in portion at 35 and 37, respectively, may be associated with, e.g., secured to, the framework 32. Various shapes and configurations for the skirt are contemplated as within the scope of the present invention. For example, the system 30 may be surrounded entirely or partially by the skirt and the skirt maybe positioned along a central axis of the system 30 or off-center relative to a central axis. Thus, the scope of the present invention as claimed herein is not limited by the shape or size of the skirt. Furthermore, in other aspects, the materials 34 and 36 may be separated by one skirt that is positioned in any defined region between the materials 34 and 36.

Referring now to FIG. 4, in another aspect, the systems 12 and 22 of FIGS. 2A and 2B, respectively, are shown in more detail as system 40. The system 40 includes a framework 42. The framework 42 is similar to the framework 32 of FIG. 3. In this aspect of the system 40, a digestible or dissolvable material 44 is deposited on a portion of one side of the framework 42. At a different portion of the same side of the framework 42, another digestible material 46 is deposited, such that materials 44 and 46 are dissimilar. More specifically, materials 44 and 46 are selected such that they form a voltage potential difference when in contact with a conducting liquid, such as body fluids. Thus, when the system 40 is in contact with and/or partially in contact with the conducting liquid, then a current path, an example is shown in FIG. 5, is formed through the conducting liquid between material 44 and 46. A control device 48 is secured to the framework 42 and electrically coupled to the materials 44 and 46. The control device 48 includes electronic circuitry that is capable of controlling part of the conductance path between the materials 44 and 46. The materials 44 and 46 are separated by a non-conducting skirt 49. Various examples of the skirt 49 are disclosed in U.S. Provisional Application No. 61/173,511 filed on Apr. 28, 2009 and entitled “HIGHLY RELIABLE INGESTIBLE EVENT MARKERS AND METHODS OF USING SAME” also filed as PCT Application No. PCT/US10/32590 dated Apr. 27, 2010 and published as WO 2010/129288 . . . dated Nov. 11, 2010 and U.S. Provisional Application No. 61/173,564 filed on Apr. 28, 2009 and entitled “INGESTIBLE EVENT MARKERS HAVING SIGNAL AMPLIFIERS THAT COMPRISE AN ACTIVE AGENT” also filed as PCT Application No. PCT/US10/32590 dated Apr. 27, 2010 and published as WO 2010/129288 . . . dated Nov. 11, 2010; as well as U.S. application Ser. No. 12/238,345 filed Sep. 25, 2008 and entitled “IN-BODY DEVICE WITH VIRTUAL DIPOLE SIGNAL AMPLIFICATION” and published as 2009-0082645 A1 dated Mar. 26, 2009; the entire disclosure of each is incorporated herein by reference.

Once the control device 48 is activated or powered up, the control device 48 can alter conductance between the materials 44 and 46. Thus, the control device 48 is capable of controlling the magnitude of the current through the conducting liquid that surrounds the system 40. As indicated above with respect to system 30, a unique current signature that is associated with the system 40 can be detected by a receiver (not shown) to mark the activation of the system 40. In order to increase the “length” of the current path the size and/or characteristics of the skirt 49 is altered. The longer the current path, the easier it may be for the receiver to detect the current.

Referring now to FIG. 5, the system 30 of FIG. 3 is shown in an activated state and in contact with conducting liquid. The system 30 is grounded through ground contact 52. For example, when the system 30 is in contact with a conducting fluid, the conducting fluid provides the ground. The system 30 also includes a sensor module 74, which is described in greater detail with respect to FIG. 6. Ion or current paths 50 are formed between material 34 to material 36 and through the conducting fluid in contact with the system 30. The voltage potential created between the material 34 and 36 is created through chemical reactions between materials 34/36 and the conducting fluid.

The system 30 also includes a unit 75. The unit 75 includes aspects that enable communication functions and in accordance with the various aspects of the present invention can act as any of the following: a receiver, a transmitter, or a transceiver. Thus, another device that is external to the system 30, such as a cell phone, an implanted device, a device attached to the user's body, or a device placed under the user's skin, may communicate, e.g. to, from or both, the system 30 through the unit 75. The unit 75 is also electrically connected to the materials 34 and 36. In accordance with one aspect of the present invention, any device that is external to the system 30 may communicate with either the unit 75 or the control module 38 using current flow through the environment surrounding the system 30. For example, a patch or receiver that is attached to the user's body, a cell phone or device being held by the user, or an implanted device, are examples of devices which can generate a current signature through the user's body. The current signature can include information that is encoded therein. The current signature is detected by the system 30, using the unit 75 or the control module 38, and decoded to allow communication to the system 30 from the device external to system 30. Accordingly, the external device can send a signal to the unit 75, either wirelessly or through transconduction, that controls the activation of the system 30.

In accordance with one aspect of the present invention, the unit 75 can also measure the surrounding environment, either directly or through the sensor module 74, to determine is the system 30 should be deactivate due to unfavorable environmental conditions. For example, the unit 75 may include an impedance measurement unit 75 a that is able to measure impedance of the environment around the system 30. The unit 75 a measures impedance by transmitting or applying voltage to one output terminal, such as the material 34. The unit 75 a then measures impedance (using the resistance 31 of FIG. 3). With a known quantity of resistance and the known voltage, the unit 75 a is able to determine the impedance of the surrounding environment. The received signal at the receiver is directly proportional to the current output of the system 30. If a variable resistance is added at the output terminal of the system 30, such as resistance 31, then the current output of the system 30 will be proportional to 1/(R+Z), where R is the value of the variable resistor and Z, the local impedance of the solution or stomach environment around the system 30. Therefore, the detected signal will be equal to:

Vreceievd=k/(R+Z)

The system 30 can be designed with a variable resistor that cycles between 2 or more levels during transmission. This results in a received signal that will vary according the above equation. When detected, the signal is used to generate a linear plot to fit:

1/Vreceived vs R

and determine the slope and intercept. The slope will have a value 1/k and the intercept, Z/k. This allows both k and the local impedance of the system 30 to be determined, independent of the actual voltage or current draw from the system 30 because the value of the variable resistor is know from the design parameters.

The impedance measurement may be used to monitor hydration state of the patient, presence of drug, Gastro-intestinal motility/waves, gastric transit time, presence of certain types of tissue (tumors) or bleeding. The impedance measurement is also a useful diagnostic tool for monitoring performance of the system 30. For example, if the impedance of the surrounding environment would prevent effective communication, then the system 30 can be deactivated or activated with a delay. In accordance with one aspect of the present invention, the unit 75 sends a signal to the control device 38. In response, the control device 38 can alter the conductance, and hence the impedance, between the materials 34 and 36 to reduce the rate of chemical reaction between materials 34 and 36 and the surrounding environment and thereby cause the system 30 to reach a deactivated mode, state, or condition. In this way, even though there is some chemical reaction, it is sufficiently low to preserve the power of the system 30 for later use, while still allowing operation of sensing and measurement of the nearby environment.

If the conditions of the environment change to become favorable to communication, as determine by the measurements of the environment, then the unit 75 sends a signal to the control device 38 to alter the conductance between the materials 34 and 36 to allow for communication using the current signature of the system 30. Thus, if the system 30 has been deactivated and the impedance if the environment is suitable for communication, then the system 30 can be activated again.

If the conditions of the environment change to become favorable to communication, as determined by the measurements of the environment, then the unit 75 sends a signal to the control device 38 to alter the conductance between the materials 34 and 36 to allow for communication using the current signature of the system 30. Thus, if the system 30 has been deactivated and the impedance of the environment is suitable for communication, then the system 30 can be activated again.

Referring now to FIG. 5A, this shows an exploded view of the surface of the material 34. In one aspect, the surface of the material 34 is not planar, but rather an irregular surface. The irregular surface increases the surface area of the material and, hence, the area that comes in contact with the conducting fluid. In one aspect, at the surface of the material 34, there is an electrochemical reaction between the material 34 and the surrounding conducting fluid such that mass is exchanged with the conducting fluid. The term “mass” as used here includes any ionic or non-ionic species that may be added or removed from the conductive fluid as part of the electrochemical reactions occurring on material 34. One example includes the instant where the material is CuCl and when in contact with the conducting fluid, CuCl is converted to Cu metal (solid) and Cl— is released into the solution. The flow of positive ions into the conducting fluid is depicted by the current path 50. Negative ions flow in the opposite direction. In a similar manner, there is an electrochemical reaction involving the material 36 that results in ions released or removed from the conducting fluid. In this example, the release of negative ions at the material 34 and release of positive ions by the material 36 are related to each other through the current flow that is controlled by the control device 38. The rate of reaction and hence the ionic emission rate or current, is controlled by the control device 38. The control device 38 can increase or decrease the rate of ion flow by altering its internal conductance, which alters the impedance, and therefore the current flow and reaction rates at the materials 34 and 36. Through controlling the reaction rates, the system 30 can encode information in the ionic flow. Thus, the system 30 encodes information using ionic emission or flow.

The control device 38 can vary the duration of ionic flow or current while keeping the current or ionic flow magnitude near constant, similar to when the frequency is modulated and the amplitude is constant. Also, the control device 38 can vary the level of the ionic flow rate or the magnitude of the current flow while keeping the duration near constant. Thus, using various combinations of changes in duration and altering the rate or magnitude, the control device 38 encodes information in the current or the ionic flow. For example, the control device 38 may use, but is not limited to any of the following techniques, including Binary Phase-Shift Keying (PSK), Frequency modulation, Amplitude modulation, on-off keying, and PSK with on-off keying.

As indicated above, the various aspects disclosed herein, such as systems 30 and 40 of FIGS. 3 and 4, respectively, include electronic components as part of the control device 38 or the control device 48. Components that may be present include but are not limited to: logic and/or memory elements, an integrated circuit, an inductor, a resistor, and sensors for measuring various parameters. Each component may be secured to the framework and/or to another component. The components on the surface of the support may be laid out in any convenient configuration. Where two or more components are present on the surface of the solid support, interconnects may be provided.

As indicated above, the system, such as control devices 30 and 40, control the conductance between the dissimilar materials and, hence, the rate of ionic flow or current. Through altering the conductance in a specific manner the system is capable of encoding information in the ionic flow and the current signature. The ionic flow or the current signature is used to uniquely identify the specific system. Additionally, the systems 30 and 40 are capable of producing various different unique patterns or signatures and, thus, provide additional information. For example, a second current signature based on a second conductance alteration pattern may be used to provide additional information, which information may be related to the physical environment. To further illustrate, a first current signature may be a very low current state that maintains an oscillator on the chip and a second current signature may be a current state at least a factor of ten higher than the current state associated with the first current signature.

Referring now to FIG. 6, a block diagram representation of the control device 38 is shown. The control device 38 includes a control module 62, a counter or clock 64, and a memory 66. Additionally, the device 38 is shown to include a sensor module 72 as well as the sensor module 74, which was referenced in FIG. 5. The control module 62 has an input 68 electrically coupled to the material 34 and an output 70 electrically coupled to the material 36. The control module 62, the clock 64, the memory 66, and the sensor modules 72/74 also have power inputs (some not shown). The power for each of these components is supplied by the voltage potential produced by the chemical reaction between materials 34 and 36 and the conducting fluid, when the system 30 is in contact with the conducting fluid. The control module 62 controls the conductance through logic that alters the overall impedance of the system 30. The control module 62 is electrically coupled to the clock 64. The clock 64 provides a clock cycle to the control module 62. Based upon the programmed characteristics of the control module 62, when a set number of clock cycles have passed, the control module 62 alters the conductance characteristics between materials 34 and 36. This cycle is repeated and thereby the control device 38 produces a unique current signature characteristic. The control module 62 is also electrically coupled to the memory 66. Both the clock 64 and the memory 66 are powered by the voltage potential created between the materials 34 and 36.

The control module 62 is also electrically coupled to and in communication with the sensor modules 72 and 74. In the aspect shown, the sensor module 72 is part of the control device 38 and the sensor module 74 is a separate component. In alternative aspects, either one of the sensor modules 72 and 74 can be used without the other and the scope of the present invention is not limited by the structural or functional location of the sensor modules 72 or 74. Additionally, any component of the system 30 may be functionally or structurally moved, combined, or repositioned without limiting the scope of the present invention as claimed. Thus, it is possible to have one single structure, for example a processor, which is designed to perform the functions of all of the following modules: the control module 62, the clock 64, the memory 66, and the sensor module 72 or 74. On the other hand, it is also within the scope of the present invention to have each of these functional components located in independent structures that are linked electrically and able to communicate.

Referring again to FIG. 6, the sensor modules 72 or 74 can include any of the following sensors: temperature, pressure, pH level, and conductivity. In one aspect, the sensor modules 72 or 74 gather information from the environment and communicate the analog information to the control module 62. The control module then converts the analog information to digital information and the digital information is encoded in the current flow or the rate of the transfer of mass that produces the ionic flow. In another aspect, the sensor modules 72 or 74 gather information from the environment and convert the analog information to digital information and then communicate the digital information to control module 62. In the aspect shown in FIGS. 5, the sensor module 74 is shown as being electrically coupled to the material 34 and 36 as well as the control device 38. In another aspect, as shown in FIG. 6, the sensor module 74 is electrically coupled to the control device 38 at connection 78. The connection 78 acts as both a source for power supply to the sensor module 74 and a communication channel between the sensor module 74 and the control device 38.

Referring now to FIG. 5B, the system 30 includes a pH sensor module 76 connected to a material 39, which is selected in accordance with the specific type of sensing function being performed. The pH sensor module 76 is also connected to the control device 38. The material 39 is electrically isolated from the material 34 by a non-conductive barrier 55. In one aspect, the material 39 is platinum. In operation, the pH sensor module 76 uses the voltage potential difference between the materials 34/36. The pH sensor module 76 measures the voltage potential difference between the material 34 and the material 39 and records that value for later comparison. The pH sensor module 76 also measures the voltage potential difference between the material 39 and the material 36 and records that value for later comparison. The pH sensor module 76 calculates the pH level of the surrounding environment using the voltage potential values. The pH sensor module 76 provides that information to the control device 38. The control device 38 varies the rate of the transfer of mass that produces the ionic transfer and the current flow to encode the information relevant to the pH level in the ionic transfer, which can be detected by a receiver (not shown). Thus, the system 30 can determine and provide the information related to the pH level to a source external to the environment.

As indicated above, the control device 38 can be programmed in advance to output a pre-defined current signature. In another aspect, the system can include a receiver system that can receive programming information when the system is activated. In another aspect, not shown, the switch 64 and the memory 66 can be combined into one device.

In addition to the above components, the system 30 may also include one or other electronic components. Electrical components of interest include, but are not limited to: additional logic and/or memory elements, e.g., in the form of an integrated circuit; a power regulation device, e.g., battery, fuel cell or capacitor; a sensor, a stimulator, etc.; a signal transmission element, e.g., in the form of an antenna, electrode, coil, etc.; a passive element, e.g., an inductor, resistor, etc.

In certain aspects, the ingestible circuitry includes a coating layer. The purpose of this coating layer can vary, e.g., to protect the circuitry, the chip and/or the battery, or any components during processing, during storage, or even during ingestion. In such instances, a coating on top of the circuitry may be included. Also of interest are coatings that are designed to protect the ingestible circuitry during storage, but dissolve immediately during use. For example, coatings that dissolve upon contact with an aqueous fluid, e.g. stomach fluid, or the conducting fluid as referenced above. Also of interest are protective processing coatings that are employed to allow the use of processing steps that would otherwise damage certain components of the device. For example, in aspects where a chip with dissimilar material deposited on the top and bottom is produced, the product needs to be diced. However, the dicing process can scratch off the dissimilar material, and also there might be liquid involved which would cause the dissimilar materials to discharge or dissolve. In such instances, a protective coating on the materials prevents mechanical or liquid contact with the component during processing can be employed. Another purpose of the dissolvable coatings may be provided to delay activation of the device. For example, the coating that sits on the dissimilar material and takes a certain period of time, e.g., five minutes, to dissolve upon contact with stomach fluid may be employed. The coating can also be an environmentally sensitive coating, e.g., a temperature or pH sensitive coating, or other chemically sensitive coating that provides for dissolution in a controlled fashion and allows one to activate the device when desired. Coatings that survive the stomach but dissolve in the intestine are also of interest, e.g., where one desires to delay activation until the device leaves the stomach. An example of such a coating is a polymer that is insoluble at low pH, but becomes soluble at a higher pH. Also of interest are pharmaceutical formulation protective coatings, e.g., a gel cap liquid protective coating that prevents the circuit from being activated by liquid of the gel cap.

Identifiers of interest include two dissimilar electrochemical materials, which act similar to the electrodes (e.g., anode and cathode) of a power source. The reference to an electrode or anode or cathode are used here merely as illustrative examples. The scope of the present invention is not limited by the label used and includes the aspect wherein the voltage potential is created between two dissimilar materials. Thus, when reference is made to an electrode, anode, or cathode it is intended as a reference to a voltage potential created between two dissimilar materials.

When the materials are exposed and come into contact with the body fluid, such as stomach acid or other types of fluid (either alone or in combination with a dried conductive medium precursor), a potential difference, that is, a voltage, is generated between the electrodes as a result of the respective oxidation and reduction reactions incurred to the two electrode materials. A voltaic cell, or battery, can thereby be produced. Accordingly, in aspects of the invention, such power supplies are configured such that when the two dissimilar materials are exposed to the target site, e.g., the stomach, the digestive tract, etc., a voltage is generated.

In certain aspects, one or both of the metals may be doped with a non-metal, e.g., to enhance the voltage output of the battery. Non-metals that may be used as doping agents in certain aspects include, but are not limited to: sulfur, iodine and the like.

It is to be understood that this invention is not limited to particular embodiments or aspects described herein and, as such, may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the invention.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention, representative illustrative methods and materials are now described.

All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

It is noted that, as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual aspects described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several aspects without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is readily apparent to those of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications may be made thereto without departing from the spirit or scope of the appended claims.

Accordingly, the preceding merely illustrates the principles of the invention. It will be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended to aid the reader in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and aspects of the invention as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. The scope of the present invention, therefore, is not intended to be limited to the exemplary aspects shown and described herein. Rather, the scope and spirit of present invention is embodied by the appended claims. 

1. A device for communication, the device comprising: a communication unit comprising: a support structure; a partial power source comprising: a first material deposited onto the support structure; and a second material deposited onto the support structure and electrically isolated from the first material, wherein the first material and the second material are selected to have a voltage potential difference when in contact with a conducting fluid to provide power to activate the device; a control module associated with the support structure and electrically connected to the first material and the second material for controlling the conductance between the first material and the second material such that a change in conductance between the first material and the second material alters the device's current signature and thereby encodes information in the current signature; and a unit in communication with the control module and associated with the support structure to at least either receive a signal from an external source or send a signal to the external source.
 2. The device of claim 1, further comprising a sealed housing defining a cavity, wherein the communication unit is positioned within the cavity.
 3. The device of claim 2, further comprising a release material within the cavity, wherein the unit generates a release command to cause the release material to expand and open the sealed housing.
 4. The device of claim 3, wherein the unit includes a mechanism that extends outward from the unit to penetrate a wall portion of the sealed housing and allow the communication unit to be separated from the sealed housing.
 5. The device of claim 2, wherein the unit includes a rod that is mechanically activated to tear a wall portion of the sealed housing and cause the sealed housing to open and allow the communication unit to come into contact with the conducting fluid.
 6. The device of claim 1 wherein the unit measures at least one characteristic associated with an environment immediately surrounding the communication unit.
 7. The device of claim 6 further comprising a release apparatus secured to the support structure and in communication with the unit, wherein the release apparatus receives the release command from the unit and in response to the signal causes the device to be exposed to the conducting fluid.
 8. The device of claim 7, wherein the cavity includes a material that is in communication with the release apparatus and the release apparatus causes the material to expand within the cavity such that the sealed housing breaks apart.
 9. The device of claim 7, wherein the release apparatus includes an expanding material that expands within the cavity to cause the sealed housing to break apart.
 10. The device of claim 7, wherein the release apparatus includes a rod that is mechanically extended from the release apparatus within the cavity of the sealed housing to cause the sealed housing to break apart.
 11. The device of claim 1, wherein after the device comes into contact with the conducting fluid, a signal received at the unit is sent to the control module and the control module reduces the power generated by the device by altering the conductance between the first material and the second material.
 12. The device of claim 1, wherein the unit sends information associated with the environment of the device to an external source.
 13. The device of claim 1 wherein the unit comprises an impedance measurement unit coupled to the first material at one output and coupled to the second material at another output to measure the impedance of the surrounding environment and to control the device.
 14. The device of claim 13, wherein the unit sends an impedance signal to the control module and the control module alters the conductance between the first material and the second material upon receipt of the impedance signal.
 15. The device of claim of 14 wherein the impedance measuring unit sends the impedance signal to the control module to indicate to the control module that the impedance of the surrounding environment is below the designated value and the device can be activated.
 16. The device of claim 1 wherein the unit receives a deactivate signal from an external source and communicates that information to the control module such that the control module alters the conductance between the first material and the second material in order to prevent generation of a current flow between the first material and second material and thereby deactivate the device.
 17. The device of claim 1, further comprising a sealed housing defining a cavity, wherein the communication unit is positioned within the cavity and further comprising an electroactive matrix within the cavity, wherein the unit generates voltage to cause the electroactive matrix to expand and open the sealed housing.
 18. The device of claim 1, wherein after the device comes into contact with the conducting fluid, a signal received at the unit is sent to the control module and the control module adjusts conductance in response to impedance to at least one of maintain a constant power output and maintain power above a minimum threshold.
 19. The device of claim 13, wherein after the device comes into contact with the conducting fluid, the impedance measurement is correlated to at least one indicator selected from a group consisting essentially of the following: hydration state, presence of a drug, gastro-intestinal motility/waves, gastric transit time, presence of specific tissue type, and location of specific tissue type.
 20. The device of claim 13, wherein the impedance measurement unit measures impedance at multiple frequencies. 